MIMO (Multiple-Input Multiple-Output) technology means using multiple transmitting antennas and receiving antennas to transmit and receive signals at a transmitter and a receiver, respectively, to improve the communication quality.
SM (Spatial Modulation) technology, as one of branch technologies of MIMO technology, is also a new multi-antenna transmission scheme, which introduces a spatial dimension into an information bit modulation process, so that only one transmitting antenna is in a working state to transmit data at any time slot, and a portion of the transmitted information bits are mapped to a conventional digital modulation constellation, and the remaining bits are mapped to a spatial dimension generated by the antenna serial number. The SM technology introduces the spatial dimension, increases the Euclidean distance between constellation symbols, and improves the error code performance of the system to some extent. Therefore, the SM technology has gradually become a research hotspot in the field of wireless communication.
Compared with the traditional MIMO technology, the spatial modulation technology avoids inter-channel interference and improves system performance, but its spectral efficiency may only increases in a logarithmic manner (in a non-linear manner). In addition, when the SM technology activates the antennas, the antennas need to be selected constantly. The transmitting antennas need to remain in an antenna selected state for a long time, and a delay in symbol transmission might be caused by pulse shaping upon the switching of the transmitting antennas. Therefore, the SM technology limits the fast switching of the system RF links, and is limited by a high-speed data transmission system.
In view of some drawbacks of the SM technology, the concept of quadrature spatial modulation (QSM) technology is proposed. According to the QSM technology, a real part of a transmission symbol is separated from its imaginary part. Since the QSM technology maintains the advantages of the SM technology while improving the spectrum efficiency of the system, the overhead of the system does not significantly increase.
However, it has been found from practical application that the existing communication system based on QSM technology has a relatively low transmission rate on account of a large amount of calculation, which limits the practical application of the QSM technology-based communication systems.